Recently, in the field of memory devices, three-dimensional memory cells have been drawing attention. To form such memory cells, a plurality of electrode layers functioning as control gates are stacked to form a stacked body. Memory holes are formed in the stacked body. A memory film is formed on the sidewall of the memory hole. A channel body layer is further formed in the memory hole. In this type of memory device, it is desired to further increase the number of the plurality of electrode layers in order to increase the degree of integration.
However, with the increase in the number of the plurality of electrode layers, the thickness of the stacked body increases. Thus, processing of the stacked body may cause trouble. For instance, if a deep trench is formed in the stacked body, the aspect ratio of the stacked body divided by the trench is inevitably increased. This decreases the mechanical strength of the divided stacked body, and may cause collapse of the divided stacked body.